The present invention relates to a method for controlling a gear shift operation in the drive assembly of a motor vehicle and a drive assembly for implementing the method.
Today""s motor vehicles usually have an internal combustion engine which acts upon the drive wheels of the motor vehicles via a transmission gear, whereby a transmission input shaft is coupled to an output shaft of the internal combustion engine. In order to change the gear ratio of the transmission gear (gear shift operation), the transmission input shaft and the output shaft must be separated by activating a main clutch. In most cases, this is accompanied by the disengagement of the coupling between all secondary assemblies and the transmission input shaft, including an electrical machine. Following this, a previously selected transmission ratio step can be taken out. When a new transmission ratio step is engaged, the revolutions per minute are adjusted between the transmission input shaft and a transmission output shaft (synchronization) solely by means of coupling elements, such as for instance synchronizer rings. Following the RPM adjustment, the main clutch is closed again. The disadvantage of this method is that the gear synchronization achieved by means of synchronizer rings leads to relatively high mechanical loads, accompanied by significant wear and tear to clutch elements which causes the synchronization effect to deteriorate over time.
There are known drive assemblies in which the electrical machine acts directly upon the transmission input shaft. During any change in the transmission ratio step, the electrical machine places a load in the form of an additional mass inertia on the transmission input shaft and hence on the synchronizer rings. DE 197 45 995 discloses an electrical machine that engages with a transmission input shaft through a controllable intermediate transmission. This either causes the load to be canceled when the intermediate transmission assumes a neutral position, or the RPM adjustment of the transmission input shaft and the transmission output shaft to be assisted by using an appropriate control. However, the method described in DE 197 45 995 is limited to automatic transmissions, since the shift direction is determined by an associated electronic control device. This method is unsuited for controlling manual transmissions, since the shift direction and the shift moment cannot be predicted with certainty.
The drive assembly of the present invention, as well as the method for controlling the gear shift allow for the use of an electrical machine that is connected to the transmission input shaft and assists gear synchronization in automatic and manual transmissions. The drive assembly includes at least the following components:
an internal combustion engine with an output shaft,
a manual transmission having multiple gears, and a transmission input shaft and a transmission output shaft which can be uncoupled from each other,
a main clutch which can force the transmission input shaft to actively engage with the output shaft;
an electrical machine which can be made to engage with the transmission input shaft via an intermediate transmission, and
a control unit for controlling the electrical machine and/or the intermediate transmission during gear shifting, as a function of a standard shift value sent to the transmission, and of the operating parameters and the operating size of the components.
By combining the above-listed components, the electrical machine can assist the gear shift process of a manual transmission having multiple gears. When the operator manipulates the gear shift lever for the main clutch and/or opening the main clutch, a possible standard shift value and its associated transmission ratio are predicted and the operating parameters and operating state of the electrical machine and/or the intermediate transmission are controlled during the gear shifting as a function of the possible standard shift value. This allows the mechanical load on the clutch elements to be appreciably reduced over the entire period of operation.
The possible gear shift is preferably determined by means of a characteristic diagram in which the operator""s driving style, the operating parameters, and the operating state of the components are captured. This, for example, allows the operator""s driving style to be evaluated in terms of a performance- or fuel consumption-oriented driving operation.
The operating parameters that can be considered include values such as the engine RPM, an activation signal for the gear shift lever, the transmission input and transmission output speeds, the vehicle""s traveling speed, the vehicle""s acceleration rate, the RPM of the electrical machine, and the intervals between various gear shifts. The operating states include, for example, the driving pedal positions for gas or brake, the transmission ratio of the transmission or the intermediate transmission, and the operating mode of the electrical machine or the main clutch.
It has also been found to be advantageous to include an evaluation factor in the shift characteristic table or diagram, which is adjusted as a function of agreement between the predicted transmission ratio and the selected transmission ratio (a self-learning diagram). To this end, the evaluation factor is assigned to predetermined combinations of operating parameters and/or operating states. Thus, if the transmission ratios do not agree, for instance if the evaluation factor is reduced, the invention allows the operator""s shifting style to be predicted with an increasingly higher probability as the vehicle is operated for longer periods of times.
It has also been shown to be advantageous if, in order to control gear shifting:
(a) a rated transmission input speed is determined together with the transmission input speed and the predicted transmission ratio,
(b) a comparison of the rated transmission input speed with the transmission input speed shows a deviation
(c) the deviation serves to determine and subsequently adjust the operating states of the electrical machine and the intermediate transmission, as well as the transmission ratio of the intermediate transmission,
(d) after declutching the main clutch, the transmission input speed is adjusted by means of the electrical machine to the rated transmission input speed, and
(e) the electrical machine is uncoupled if the predicted transmission ratio does not agree with the actually selected transmission ratio.
The above-described method allows the gear synchronization to be effected in a particularly secure manner.
It is especially advantageous to switch the electrical machine to generator operation in the event the RPM exceeds the rated speed. Conversely, the torque that is to be transmitted to the transmission input shaft can then be selected, in the engine mode, by specifying the RPM of the electrical machine and/or the transmission ratio of the intermediate transmission.
Additional preferred embodiments of the invention are evident from the remaining characteristics indicated in the dependent claims.